From Galileo to Darwin to Einstein, great breakthroughs were only possible when the seemingly obvious conclusions and the common sense outcomes were rejected by asking the right questions and watching the results very carefully.

One of the great joys in science is the often-unexpected way the natural world behaves.
Here is a simple demonstration you can try at home to illustrate how outcomes are not always what we expect.  In science, if the results are not what you expect, then you need to develop new explanations that will allow you to correctly predict the outcome of the same or similar activity the next time.

Water works

  • Step 1: Gather Materials

Get a resealable zipper sandwich bag (a Ziploc or equivalent).  Fill it about half full with water and seal it.  Get yourself a sharp pencil.  

  • Step 2: Take a Stab

Firmly and smoothly, push the sharp pencil into one side of the bag and out the other, through the water-filled portion, so that the pencil remains in the bag, pointy end sticking out one side and blunt end out the other.  Try it with two or three more pencils!  In most circumstances, the act of puncturing a water-filled bag with a sharp stick would result in the water pouring out the tear. Not so in this situation.

  • Step 3: Observe

You will observe the bag wrapping tightly around the sides of the pencil, keeping the bag watertight. This is a marvelous illustration of the behaviour of the very long, stretchy polyethylene molecules contracting under tension. It’s a wonderful exploration of material science.

Battling balloons

  • Step 1: Gather Materials

While we’re dealing with stretchy stuff, get yourself two balloons and a short length of tube.  I like to use a piece of 20 millimeter (one half-inch) PVC pipe, about 15-20 centimeters long. The exact dimensions and material don’t matter as long as the balloons can be stretched airtight over each end.

  • Step 2: Inflate & Connect

Attach a balloon to one end and blow through the tube to inflate it, say, about three-quarters full. Twist or clamp the neck of the balloon so air cannot escape.

Inflate another identical balloon with just a few puffs so it is partially inflated but much smaller than the first balloon. Twist or clamp its neck so no air escapes and attach it to the open end of the pipe. This is a little tricky. It requires some dexterity and practice.  So now you have two balloons connected to the pipe, with one significantly larger than the other.

With both balloons attached to the pipe, untwist them and let air pass between the two balloons.  What happens?  Which balloon gets bigger, or is there no change?

  • Step 3: Observe

The result is surprising.  The big balloon gets bigger and the small balloon gets smaller.  The typical expectation is that the two balloons will end up the same size.   The pressure inside the two balloons equalizes, but not in the way you might expect.

What is the hardest part of blowing up a balloon?  The start!  The elastic skin of the balloon is exerting the greatest resistance to inflation when in the balloon is just starting to inflate.  The pressure inwards from the balloon itself is at its maximum. 

Just another surprising twist that reminds us yet again that science is not an exercise in common sense!